Brooks Koepka is having the kind of year he only imagined in his dreams, and he’s not ready for it to end.

In June, he became the first player in 29 years to win back-to-back in the U.S. Open. In August, he played some his best golf amid ear-splitting cheers for Tiger Woods on the back nine at Bellerive to win the PGA Championship with a record score. In a span of 19 days in October, he was voted PGA Tour player of the year and won the CJ Cup in South Korea to reach No. 1 in the world.

The trick now is to stay there.

He makes his debut at No. 1 on Thursday in the HSBC Champions at Sheshan International against a top-heavy field that includes five of the six top players in the world and all the major champions from this year.

“Looking forward to teeing it as No. 1,” Koepka said. “I think that’s something every golfer kind of dreams of and every golfer wants to accomplish. I’m looking to build on that lead, grow it, and that way I can be No. 1 for a while. The goal isn’t just to get here. It’s to stay here.”

It doesn’t figure to be easy.

He replaced his good friend and neighbor, Dustin Johnson, atop the world ranking. Johnson has his own score to settle at this World Golf Championship after tying the wrong kind of record last year when he lost a six-shot lead in the final round. Justin Rose would up coming from eight shots behind to win.

Johnson and Rose each have a chance to return to No. 1 this week.

Also in the field is Rory McIlroy at No. 5 and Francesco Molinari at No. 6.

Molinari is the only player who can make a case for having the best year worldwide. Koepka has the edge with his two majors. Molinari counters with his first major at the British Open to go along with a victory at Wentworth in the European Tour flagship event, the Quicken Loans National on the PGA Tour, and if that wasn’t enough, the first European to go 5-0 in the Ryder Cup.

Koepka and Rose are in the same group in the opening two rounds, along with Tommy Fleetwood. Molinari is playing with Johnson and McIlroy in another feature group.

The only player missing from the top six is Justin Thomas, who played the last two weeks in Asia.

The HSBC Champions is a $10 million event that starts a big end to the European Tour season, where Molinari has a lead over Fleetwood in the Race to Dubai, with McIlroy trying desperately to make up ground.

It also can be a big start for the PGA Tour’s wraparound season, which began three weeks ago.

The HSBC Champions was the centerpiece of a remarkable turnaround last year for Rose, who had a stretch of 10 consecutive finishes in the top 10. That includes his unlikely victory at Sheshan International, along with victories in the Turkish Airlines Open and the Indonesia Masters.

It eventually led Rose to reaching No. 1 in the world after a runner-up finish at the BMW Championship outside Philadelphia, though the ranking lasted only two weeks before Johnson took it back.

Now it’s Koepka’s turn.

This is the first time since 1997 that four players have spent time at No. 1 in the world, and the first time since the world ranking began in 1986 that the top four in the world have all been No. 1 in the same year.

Pressure?

“I’ve only been world No. 1 for three days,” Koepka said Wednesday. “I haven’t found too many challenges in those days.”

Johnson won the HSBC Champions in 2013, and it looked as though he would add another World Golf Championships title a year ago when he had a six-shot lead. Most remarkable about that collapse was that Johnson still had a three-shot lead going to the back nine, didn’t miss a fairway and still lost.

But he got over it quickly, winning his next PGA Tour start at Kapalua by eight shots.

Then again, no one is more equipped at handling mishaps than Johnson, who has a history of having bad things happen at big events.

“A lot of practice,” he said with a smile. “Whether I’m playing at home or out here, you’re going to make mistakes. It just happens. I think it just all depends on how you handle them and if you let it bother you.”

Johnson is playing his only event in the fall. For Koepka, it’s his final event of a year that he hopes has one more trophy.